Everything is Awesome, Everything is Cool When You Are Part of a Team! –Lego Movie
The LEGO head or mask for a LEGO costume does not seem to be readily available from retailers, so you are in for a few hours of DIY if you want a Lego costume.
The couple from their tutorial here said they spent over 12 hours on their Lego costumes, so be prepared for a trip to Home Depot, cutting, gluing, painting, and drying time. It is worth it because their Lego heads turned out very authentic!
They said they got their instructions from this tutorial here from Instructables.com which has a ton of helpful tips in the comments.
If you allow enough prep time or have lots of help, this is a super family or group costume!
For more ideas, tips, and photos, follow The Costume Resource on Facebook.